1. Field of the Invention
The present invention relates to an image forming apparatus provided with a so-called inner finisher.
2. Related Art
In recent years, development of apparatuses using front access systems and built-up systems as a part of compact design of image forming apparatuses has been advancing.
In image forming apparatuses using a front access system, operation of an operating portion (also including a display portion), opening and closing of an opening/closing door, replenishment of paper in a feed portion, and extraction of paper from a discharge portion can all be performed from the front side of the apparatus. Also, such apparatuses are configured so that with the exception of replenishing paper in the feed portion, it is not necessary for a user to change their posture in front of the apparatus.
In image forming apparatuses using a built-up system, a configuration is adopted in which a feed portion is disposed in the lowest portion of the apparatus main body, a print portion is disposed above the feed portion, a discharge portion is disposed on the top face or a side face of the print portion, and an original reading device is disposed above those portions; that is, in the uppermost portion of the apparatus. Such apparatuses are configured so that it is possible to avoid paper jams by forming a paper transport path, that transports paper housed in the feed portion to the discharge portion via the print portion, in an approximately perpendicular upward direction. Further, by building up a plurality of feed portions, it is possible to print to paper with a plurality of sizes.
Also, in recent years, in order to achieve multiple functions in the image forming apparatus, development of paper post-processing apparatuses, in which paper post-processing such as staple processing, punch processing, and binding processing are performed, has been advancing. Paper post-processing apparatuses are also being installed in image forming apparatuses that employ a front access system and a built-up system as described above
However, for example, as disclosed in JP 2004-145200A, in an image forming apparatus using a built-up system, designing a paper post-processing apparatus on the side face of the image forming apparatus main body leads to enlargement of the apparatus as a whole, and is contrary to demands for a more compact apparatus. Thus, development of so-called inner-finisher paper post-processing apparatuses has been advancing. Specifically, a paper post-processing apparatus is not disposed outside of the image forming apparatus, and by disposing the paper post-processing apparatus together with the discharge portion in a space formed within the apparatus, an attempt is made to achieve a more compact apparatus.
However, image forming apparatuses provided with a conventional inner finisher have the following sorts of problems.
When the inner finisher is provided with a staple function, a staple processing stage used when performing staple processing is provided on the upstream side of the discharge portion. When staple processing is performed, paper for which printing is finished is discharged in order to the staple processing stage. Then, after paper adjustment, staple processing is performed, and after staple processing, a paper batch is collectively discharged to a discharging means from a pair of discharge rollers. On the other hand, when staple processing is not performed, paper for which printing is finished is discharged page by page to the discharging means from the discharge rollers via the staple processing stage.
However, as described above, when the inner finisher is provided using a space formed within the image forming apparatus, and a staple function is also provided, because it is necessary to provide both the above-mentioned staple processing stage and the discharging means in that space, the length of the staple processing stage in the paper discharge direction (the paper transport direction) may become shorter than the length in the paper transport direction of the paper for which staple processing is attempted. In such a case, there is the problem that with the pair of discharge rollers that discharge the paper to the discharging means from the staple processing stage in a contact state, staple processing cannot be performed for paper that is longer than the length of the staple processing stage in the paper discharge direction.
Also, paper is discharged to the discharging means by the pair of discharge rollers, but when one of the pair of rollers is made a drive roller and the other is made an idler roller, it is possible to discharge paper page by page from the discharge rollers to the discharging means when staple processing is not performed in the inner finisher. However, when staple processing is performed in the inner finisher, the following sort of problems occur when discharging a paper batch from the discharge rollers after staple processing. With respect to paper that is in contact with the drive roller, it is possible to confer transport force in the paper transport direction with rotation of the drive roller, but on the other hand, with respect to paper that is not in contact with the drive roller, it is not possible to confer sufficient transport force in the paper transport direction. As a result, there is the problem that only paper that is in contact with the drive roller is transported, and the paper is torn at the staple portion that binds the paper batch together. This sort of problem is more likely to occur as the number of pages of paper bound by the staple processing increases.
Further, when the inner finisher is also provided with a shifter function, it is convenient from the point of view of making the apparatus more compact, decreasing the number of members, and decreasing cost if the above-mentioned discharge rollers that discharge paper from the staple processing stage to the discharging means are also used as shifter rollers that execute shifter processing.